I had this exact same problem with my Focus over the last 4 weeks. Thought it might have been due to the hot days here in Perth and the fuel evaporating from the injectors and hence on the next start up, insufficient fuel instantaneously. But it starting happening on the cooler days, so thought must be something else.
Actually took it to Ford yesterday and i was in and out in about 1 hour, because there was a
TSB (Technical Service Bulletin) on the exact problem which saw the patch for start up which controlled timing and ignition bugger up, hence hard starting hard, but running fine after.
A reflash of the
ECU and i was on my way.
Not a problem since.
Tom